Screening apparatus

ABSTRACT

Screening apparatus of the type employed for screening pulp stock wherein diluent fluid is supplied adjacent the accepted stock face of the screen for diluting the accepted stock and causing it to flow in a direction counter to the flow of stock along the feed face of the screen.

United States Patent John P. Rich Nashua, N.

Jan. 9, 1970 June I, 1971 Improved Machinery Inc.

Nashua, NJ-l.

Continuation of application Ser. No. 695,027, Jan. 2, 1968, nowabandoned.

Inventor Appl No. Filed Patented Assignee SCREENING APPARATUS 8 Claims,5 Drawing Figs.

u.s.c1 209/273,

209/283. 209/306, 210/412, 210/415 1m. 0 801d 29/38 Field ofSearch210/409,

References Cited UNITED STATES PATENTS Clarke Lang et al... Merrill 1Pounder Rosaen Primary Examiner-John Adee Attorney-Robert R. Paquin209/273 210/409 209/273 210/415X 2l0/415X ABSTRACT: Screening apparatusof the type employed for screening pulp stock wherein diluent fluid issupplied adjacent the accepted stock face of the screen for diluting theaccepted stock and causing it to flow in a direction counter to the flowof stock along the feed face of the screen.

PATENTEU JUN 1 (97! SHEET 1 [1F 2 INVENTOR JOHN R RICH ATTORNEYPATENTEUJUN 1197: 3,581,893

SHEET 2 OF 2 INVENTOR JOHN P /'?/C/'/ ATTORNEY SCREENING APPARATUS Thisapplication is a continuation of application Ser. No. 695027 filed .Ian.2, 1968, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to apparatusfor screening mixtures of fibrous material and liquid and has moreparticular reference to screening apparatus of the type employed forscreening pulp stock during the manufacture of paper.

Conventionally, screening apparatus of the aforementioned type hasincluded a pulp screen, generally formed from a perforated or slottedmetal plate, andhas usually been constructed to cause relative vibrationbetween the pulp screen and the pulp stock. This relative vibration maybe induced by pulsing the screen, pulsing the accepted pulp stock,pulsing the feed pulp stock, or by rapidly moving a bar or airfoiladjacent a face of the screen to produce a pressure and/or suction waveadjacent the surface of the screen. The relative vibration has, ofcourse, proven to be particularly beneficial to prevent the feed stockfrom dewatering and forming a mat such as could cause blinding of thescreen.

However, in conventional screening apparatus of the aforementioned type,the relative vibration has been found to create additional problems.More specifically, in such conventional screening apparatus, therelative vibration has frequently returned through the screen anundesirably large quantity of accepted stock. This return of theaccepted stock, when it occurs adjacent the inlet end of the screen(i.e. the end of the screen initially receiving the feed stock), isobjectionable due to its adverse effects on the net throughput of thescreening apparatus. This return of the accepted stock, when it occursadjacent the discharge or rejects end of the screen (i.e. the end of thescreen discharging the rejected material), is, of course, undesirable inthat it reintroduces a quantity of accepted stock into the rejectedmaterial and thereby necessitates that the latter be rescreened torecover this accepted stock. 7

An object of the present invention is to provide a screening apparatuswhich includes new and improved means for substantially minimizing thequantity of accepted stock which is returned through the screen duringthe aforedescribed relative vibration.

Another object of the invention is to provide a screening apparatusincluding new and improved means of the type set forth which isparticularly constructed and arranged for substantially minimizing thequantity of accepted stock returned through the screen adjacent the endsof the latter.

SUMMARY OF THE INVENTION The aforegoing objects, and those other objectsand advantages of the invention which will be apparent from thefollowing description taken in connection with the accompanyingdrawings, may be attained by the provision of a screening apparatuswhich, generally considered, comprises a screen having feed and acceptsfaces and screening apertures extending therebetween, stock supply meansoperatively associated with the screen for supplying pulp stock to thescreen feed face at one end of the screen, first discharge meansoperatively associated with the screen and communicating with the stocksupply means for discharging stock rejected by the screening aperturesfrom the screen feed face at the other end of the screen, wall meansextending along the screen bounding a passage which extends along theaccepts face of the screen to receive the stock accepted by thescreening apertures, dilution liquid supply means connected to thepassage for supplying dilution liquid to the passage at said other endof the screen whereby the dilution liquid interrnixes with the acceptedstock and causes the latter to flow along the screen accepts facetowards said one end of the screen, and second discharge means connectedto the passage for discharging a mixture of dilution liquid and acceptedstock from the passage at said one end of the screen.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. II is a fragmentary, elevationalsectional view of a rotary screening apparatus including an embodimentof the present invention;

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1, looking in thedirection of the arrows;

FIG. 3 is a sectional view taken on line 3-3 of FIG. I, looking in thedirection of the arrows;

FIG. is a fragmentary, elevational sectional view of a screeningapparatus including a planar screen in combination with an embodiment ofthe present invention; and

FIG. 5 is a sectional view taken on line 5-5 of FIG. 4, looking in thedirection of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly tothe drawings wherein similar reference characters designatecorresponding parts throughout the several views, FIGS. 1 through 3illustrate a rotary screening apparatus designated generally as 10 whichcomprises a housing or casing 12 mounted by bolts 13 upon a foundationor support 14. The casing 12 is formed to include a horizontallydisposed, annular sidewall 16 and a pair of end walls 118, 20 rigidlyconnected to the opposing ends of the sidewall 16. The end of thesidewall 16 adjacent the end wall 20 includes a plurality of arcuatelyspaced, integrally formed, inlet conduits 22 which are each connectedthrough suitable conventional piping, shown fragmentarily as 24, to asource (not shown) of the pulp stock to be screened by the screeningapparatus 10. The end of the sidewall 16 adjacent the end wall 18includes an integrally formed, outlet conduit 26 which is connectedthrough suitable conventional piping, shown fragmentarily as 28, todischarge rejected material from the screening apparatus 10. The endwall 20 includes an integrally formed, outlet conduit 30, connectedthrough suitable conventional piping 32, for discharging the screenedpulp stock produced during the operation of the screening apparatus 10.

The casing 12 contains a horizontally disposed, annular screen plate 34which is rigidly supported at its opposing ends by the end walls 18, 20and concentrically arranged with the sidewall 16 to provide an annularfeed space or fluid passage 36 between the screen plate 34 and thesidewall 16. The screen plate 34 includes a circumferential, outer orfeed side face 38, a circumferential, inner accepts or accepted stockside face 40, and a plurality of screening openings or apertures 42extending between the side faces 38, 40.

A rotor 44 is located within the casing 12 internally of the screenplate 34 and rotatably supported by a hub 46 formed on the end wall 20.The rotor 44 in constructed to include an annular sidewall 48,concentric with the sidewall 16 of the easing 12, which is spaced fromthe accepted stock face 40 of the screen plate 34 to provide an annularaccepts space or fluid passage 50 between the sidewall 48 and theaccepted stock face 40. The outer circumference of the sidewall 48 isconstructed to include a plurality of protrusions 52 which are spaced bypockets 54. The protrusions 52 and pockets 54, as will be understood,cooperate in a conventional manner to pulse stock in the annular space50 during the rotation of the rotor 44. The opposing ends of thesidewall 48 of the rotor 44, as illustrated in FIG. 1, are closed by endwalls 56, one of which includes an integral stub shaft 58 rotatablysupported by the aforementioned hub 46,

The rotor 44 includes an internal, annular mounting flange 60 whichcarries a hub 62 at its inner end. The rotor 44 is supported by adriving shaft 64 which extends through aligned openings 66, 68 in theend wall 18 of the casing 12 and one of the end walls 56 of the rotor44, respectively, and is splined to the hub 62. The driving shaft 64 isconnected through suitable conventional reduction gearing (not shown) toa driving motor 74 to be rotatably driven by the latter.

The present invention, as applied to the screening apparatus 10,comprises the provision of new and improved means for substantiallyreducing the quantity of screened pulp stock driven back through thescreening apertures 42 during the rotation of the rotor 44. Morespecifically, as illustrated in FIG. 1, the end wall 18 of the casing 12is provided with an integrally formed, inlet conduit 76. The inletconduit 76 is connected through suitable conventional piping, shownfragmentarily as 78, to a source (not shown) of a diluent fluid, such asclean water, to continuously receive diluent fluid from such source. Thediluent fluid supplied through the inlet conduit 76 flows into theannular space 50 and therethrough towards the outlet conduit 30. Thisflow of the diluent fluid causes it to dilute the accepted stockadjacent the accepted stock face 40 and to cause the resultant dilutedaccepted stock to flow along the accepted stock face 40 in a directioncounter to the flow of feed stock along the feed face 38 of the screenplate 34. This dilution of the accepted stock, as will be understood,substantially reduces the quantity of accepted stock driven back throughthe screening apertures 42 during the backward flow portions of thecyclic pulses produced by the rotation of the rotor 44. Moreover, as theflow of the diluted accepted stock is counter to the flow of feed stockalong the feed face 38 of the screen plate 34, the accepted stockflowing into the annular space 50 through the screening apertures 42 atthe opposing ends of the screen plate 34 is substantially immediatelyremoved from adjacent the ends of the screen plate 34. Thus, the largequantity of stock accepted by the screening apertures 42 at the inletend (i.e. the end adjacent the inlet conduits 22) of the screen plate 34is prevented from returning through the screening apertures 42; and thestock accepted by the screening apertures 42 adjacent the discharge end(i.e. the end adjacent the outlet conduit 30) of the screen plate 34 isprevented from intermixing with the rejected material at such end of thescreen plate 34.

In the operation of the screening apparatus 10, the rotor 44 iscontinuously rotated to pulse the accepted stock in the annular space 50whereby, during the forward flow portion of each pulse, stock flowsthrough the screening apertures 42 into the annular space 50 and, duringthe backward flow portion of each pulse, stock from the annular space 50is returned through the screening apertures 42 to dilute the feed stockin the annular space 36. The feed stock is introduced into the annularspace 36 adjacent the end wall 20 through the inlet conduits 22 andflows along the feed face 38 towards the end wall 18. During this flowof the feed stock, a portion of the latter is accepted by the screeningapertures 42 and flows into the annular space 50. The portion of thefeed stock rejected by all of the screening apertures 42 is, however,discharged from adjacent the end wall 18 through the outlet conduit 26.

The diluent fluid which is introduced into the casing 12 through theinlet conduit 76 flows through the annular space 50 towards the end wall20. This flow of the diluent fluid causes it to become intermixed withthe accepted stock in the annular space 50 and dilutes the acceptedstock. Thus, the stock which is driven back through the screeningapertures 42 by the rotation of the rotor 44 is of much lowerconsistency, relative to the consistency of the feed stock, than inconventional screening apparatus wherein the accepted stock isundiluted. In addition, the diluent fluid flowing through the annularspace 50 causes the aforementioned mixture of diluent fluid and screenedpulp stock to flow towards the end wall 20 of the casing 12. As aresult, this flow of the diluent fluid substantially immediately removesthe portions of the accepted stock discharged by the screening apertures42 nearest the opposing ends of the screen plate 34 to greatly minimizethe quantity of the accepted stock driven back through the screeningapertures 42 at these locations. The mixture of diluent fluid andaccepted stock which is discharged from the annular space 50 flows fromthe screening apparatus through the outlet conduit 30 and the piping 32which is connected thereto.

FIGS. 4 and 5 illustrate an embodiment of the present invention asapplied to a screening apparatus, designated generally as 80, whichincludes a flat or planar screen plate 82. As illustrated in FIGS. 4 and5, the screen plate 82 is peripherally supported by a rigid,imperforate, boxlike supporting structure 84. The screen plate 82,similarly to the aforedescribed screen plate 34, includes a feed sideface 86, an accepts or accepted stock side face 88, and a plurality ofscreening openings or apertures 90 extending between the side faces 86,88.

The screening apparatus includes an inlet conduit 92, communicating witha source (not shown) of the pulp stock to be screened, for supplyingstock to the inlet end of the feed face 86 of the screen plate 82, andan outlet conduit 94 for discharging stock rejected by the screeningapertures from the opposing or discharge end of the feed face 86. Thescreening apparatus 80, moreover, includes a rigid, imperforate plate96, located adjacent the accepted stock face 88, which is peripherallysealed by a diaphragm 98 formed of resilient material. The plate 96 andthe diaphragm 98, as illustrated in FIGS. 4 and 5, cooperate with thescreen plate 82 to define an accepts or fluid passage 100 which extendsalong the accepted stock face 88 throughout the length and width of thescreen plate 82. The plate 96 is pivotably connected to one end of alink or connecting member 102, the opposing end of which is pivotablyconnected to a crank 104. The crank 104 is mounted upon a shaft 106which is connected through suitable conventional reduction gearing (notshown) to a driving motor 108 to be rotatably driven by the latter.

An inlet conduit 110, connected to a source (not shown) of a diluentfluid such as clean water to continuously receive diluent fluid fromsuch source, communicates with the end of the fluid passage 100 adjacentthe outlet conduit 94. An outlet conduit 112 communicates with the endof the fluid passage 100 adjacent the inlet conduit 92 for dischargingfluid from the fluid passage 100.

In the operation of the aforedescribed screening apparatus 80, the motor108 is operated to cause the plate 96 to be continuously oscillated andthereby pulse the pulp stock in the fluid passage 100 to provide theaforementioned relative vibration. The pulp stock to be screened flowsfrom the inlet conduit 92 and along the feed face 86 through the feedpassage bounded by the face 86 and the walls adjacent the sides of thescreen 82 towards the outlet conduit 94. During this flow of the pulpstock, a portion of the stock is accepted by the screening apertures 90during the forward flow portion of each pulse cycle of the plate 96 andflows into the fluid passage 100. The portion of the pulp stock rejectedby all of the screening apertures 90 is, however, discharged from thefeed face 86 through the outlet conduit 94. The diluent fluid introducedinto the fluid passage 100 through the inlet conduit 110 flows throughthe fluid passage 100 towards the outlet conduit 112. During thiscounterflow of the diluent fluid, it intermixes with the accepted stockin the fluid passage 100 and dilutes such accepted stock. Thus, duringthe reverse flow portion of each pulse cycle of the plate 96, a portionof this diluted stock flows back through the screening apertures 90 todilute the feed stock. The diluted pulp stock is discharged from thefluid passage 100 through the outlet conduit 112.

From the aforegoing, it will be seen that l have provided a screeningapparatus which includes new and improved means for substantiallyminimizing the quantit; of screened pulp stock returned through thescreen during the aforedescribed relative vibration of the latter. Itwill also be seen that this new and improved means is particularly tffcctive in preventing the return through the screen of accepted stockadjacent the opposing ends of the screen. It will be understood,however, that, although I have hereinbefore illustrated and specificallydescribed only two embodiments of my invention, my invention is notlimited merely to these illustrated and described embodiments but rathercontemplates other embodiments and variations employing the concepts andteachings of my invention.

Having thus described my invention, 1 claim:

1. An apparatus for screening pulp stock, comprising a screen havingfeed and accepts faces and screening apertures extending from said feedface to said accepts face, stock supply means at one end of said screencommunicating with a source of pulp stock and operatively associatedwith said screen for supplying pulp stock to said feed face at said oneend of said screen, rejected stock discharge means at the other end ofsaid screen communicating with said stock supply means for dischargingstock rejected by said screening apertures from said feed face at theother end of said screen, wall means extending along said accepts facecooperating therewith to bound a passage which extends continuouslyalong said accepts face in communication with said screening aperturesto receive accepted stock therefrom, dilution liquid supply meanscommunicating with a source of dilution liquid and connected to saidpassage at said other end of said screen independently of said screeningapertures for supplying dilution liquid to said passage at said otherend of the screen, said wall means directing such dilution liquidthrough said passage along said accepts face towards said one end ofsaid screen whereby the dilution liquid intermixes with accepted stockin said passage to cause such accepted stock to flow along said acceptsface towards said one end of said screen, and accepted stock dischargemeans connected to said passage at said one end of said screen fordischarging the mixture of dilution liquid and accepted stock from saidpassage at said one end of said screen.

2. A screening apparatus according to claim 1, wherein said screen is aflat screen and said wall means includes means operable for pulsing themixture in said passage.

3. A screening apparatus according to claim 1, wherein said screen isannular, and said wall means is also annular whereby said passage isannular.

4. A screening apparatus according to claim 1, wherein said screen isannular with said feed and accepts faces being the outer and inner facesof said screen, respectively, said wall means is annular and disposedwithin said screen whereby said passage is annular, and means areprovided for pulsing the mixture in said passage.

5. A screening apparatus according to claim 4, wherein said pulsingmeans is carried by said wall means and said wall means and screen arerelatively rotatable.

6. An apparatus for screening pulp stock, comprising a screen havingfeed and accepts faces and screening apertures extending therebetween,stock supply means communicating with a source of pulp stock andoperatively associated with said screen for supplying pulp stock to saidfeed face at one end of said screen, first discharge means operativelyassociated with said screen and communicating with said stock supplymeans for discharging stock rejected by said screening apertures fromsaid feed face at the other end of said screen, second discharge meansoperatively associated with said screen for discharging accepted stockfrom adjacent said accepts face at said one end of said screen, dilutionliquid supply means communicating with a source of dilution liquid andon the accepts side of said screen for supplying dilution liquid to saidaccepts face at said other end of said screen independently of saidscreening apertures, and means extending along said screen bounding aspace which extends continuously along said accepts face from said oneend of said screen to said other end thereof, said space communicatingwith said screening apertures to receive stock accepted thereby and saidspace connecting said dilution liquid supply means with said seconddischarge means whereby dilution liquid supplied to said dilution liquidsupply means flows along said accepts face towards said one end of saidscreen and intermixes with accepted stock in said space to cause suchaccepted stock to flow along said accepts face to said second dischargemeans.

7. A screening apparatus according to claim 6, wherein said screen is aflat screen, and said feed and accepts faces are the upper and lowerfaces, respectively, of said screen.

8. A screening apparatus according to claim 6, wherein said screen andspace are annular.

1. An apparatus for screening pulp stock, comprising a screen havingfeed and accepts faces and screening apertures extending from said feedface to said accepts face, stock supply means at one end of said screencommunicating with a source of pulp stock and operatively associatedwith said screen for supplying pulp stock to said feed face at said oneend of said screen, rejected stock discharge means at the other end ofsaid screen communicating with said stock supply means for dischargingstock rejected by said screening apertures from said feed face at theother end of said screen, wall means extending along said accepts facecooperating therewith to bound a passage which extends continuouslyalong said accepts face in communication with said screening aperturesto receive accepted stock therefrom, dilution liquid supply meanscommunicating with a source of dilution liquid and connected to saidpassage at said other end of said screen independently of said screeningapertures for supplying dilution liquid to said passage at said otherend of the screen, said wall means directing such dilution liquidthrough said passage along said accepts face towards said one end ofsaid screen whereby the dilution liquid intermixes with accepted stockin said passage to cause such accepted stock to flow along said acceptsface towards said one end of said screen, and accepted stock dischargemeans connected to said passage at said one end of said screen fordischarging the mixture of dilution liquid and accepted stock from saidpassage at said one end of said screen.
 2. A screening apparatusaccording to claim 1, wherein said screen is a flat screen and said wallmeans includes means operable for pulsing the mixture in said passage.3. A screening apparatus according to claim 1, wherein said screen isannular, and said wall means is also annular whereby said passage isannular.
 4. A screening apparatus according to claim 1, wherein saidscreen is annular with said feed and accepts faces being the outer andinner faces of said screen, respectively, said wall means is annular anddisposed within said screen whereby said passage is annular, and meansare provided for pulsing the mixture in said passage.
 5. A screeningapparatus according to claim 4, wherein said pulsing means is carried bysaid wall means and said wall means and screen are relatively rotatable.6. An apparatus for screening pulp stock, comprising a screen havingfeed and accepts faces and screening apertures extending therebetween,stock supply means communicating with a source of pulp stock andoperatively associated with said sCreen for supplying pulp stock to saidfeed face at one end of said screen, first discharge means operativelyassociated with said screen and communicating with said stock supplymeans for discharging stock rejected by said screening apertures fromsaid feed face at the other end of said screen, second discharge meansoperatively associated with said screen for discharging accepted stockfrom adjacent said accepts face at said one end of said screen, dilutionliquid supply means communicating with a source of dilution liquid andon the accepts side of said screen for supplying dilution liquid to saidaccepts face at said other end of said screen independently of saidscreening apertures, and means extending along said screen bounding aspace which extends continuously along said accepts face from said oneend of said screen to said other end thereof, said space communicatingwith said screening apertures to receive stock accepted thereby and saidspace connecting said dilution liquid supply means with said seconddischarge means whereby dilution liquid supplied to said dilution liquidsupply means flows along said accepts face towards said one end of saidscreen and intermixes with accepted stock in said space to cause suchaccepted stock to flow along said accepts face to said second dischargemeans.
 7. A screening apparatus according to claim 6, wherein saidscreen is a flat screen, and said feed and accepts faces are the upperand lower faces, respectively, of said screen.
 8. A screening apparatusaccording to claim 6, wherein said screen and space are annular.